Known curable compositions, such as epoxy resin compositions, are normally used as sealing and adhesive agents for connection and sealing of elements in electric and electronic devices. In a cured form, however, such compositions possess high modulus of elasticity and therefore have high rigidity. Therefore, when such seals are subject to thermal expansion, they develop high stress in respective elements of electric and electronic devices. This stress causes the aforementioned elements and substrates to warp, leads to formation of cracks in the cured resin itself, or even damages the electric and electronic elements, or forms gaps between the electric, electronic elements and the seals.
It has been proposed to reduce the stress generated in cured resins of the aforementioned type by utilizing a curable resin composition in which a curable resin is combined with an epoxy-containing silicone resin (see Japanese Unexamined Patent Publication [hereinafter referred to as Kokai] H5-29504, equivalent to U.S. Pat. No. 5,530,075), die-attach pastes prepared from the reaction product of an epoxy resin, cyanate resin, and an epoxy-containing dimethylsiloxane compound (see Kokai H10-147764 and Kokai H10-163232), die-bonding materials such as reaction products of an epoxy-containing silicone oil and a phenol-type organic compound (see Kokai H7-22441, Kokai H7-118365, and H10-130465), etc. However, cured bodies obtained from such a composition still remain relatively rigid, show insufficient stress-reduction effect, and find only limited application for sealing and connecting electronic and electric elements.
On the other hand, cured products obtained from curable silicone resin compositions are characterized by excellent electrical characteristics such as dielectric properties, volume resistivity, insulation breakdown strength, etc., and therefore they find application as seals and adhesives for electrical parts and electrical and electronic elements. However, the aforementioned curable silicone compositions produce cured objects that are either too soft and possess high thermal expansion, or have low strength and modulus of elasticity. Therefore, they cannot provide sufficient protection for electric and electronic parts, e.g., against externally applied impacts. Another disadvantage of curable silicone compositions is low adhesion of cured objects produced from these compositions to various electrical and electronic elements. This drawback leads to delamination of the aforementioned cured objects from the respective electric and electronic elements. Attempts have been made to reduce thermal expansion of the soft cured bodies by combining the composition with various fillers, but addition of the fillers led to sharp increase in the modulus of elasticity, so that the cured bodies were produced with impaired softness and elasticity. In other words, the effect of improvement was insufficient.
It has been proposed in Kokai H6-306084 to use a curable silicone resin composition with a shortened time of gelling. This composition consists of an epoxy-modified silicone oil and a phenol-modified silicone oil. Such a composition, however had poor curability and required a prolonged time for curing.